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Emission spontanée Spontaneous decaywith We haveWhen 2P => 1S We can rewrite it as is the flux per m 2 and per seconde of ephemeral photons falling upon the excited atom. is the number of these photons per m 3 and is the cross section for the stimulation to happen. On adopte cette densité pour notre traitement de leffet Casimir Nous obtenons la densité de photons éphémères mais seulement jusquà des énergies de quelques dizaines deV. Lémission spontanée = émission stimulée par des photons éphémères du vide.

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Effet Casimir A B C IVIIIIII P1P2 1- P1 absorbs the ephemeral photon coming from A => region I does not act upon P2 2- regions II and III cancel each other => null result on P2 3- region IV, only, acts upon P2 suppose the density of ephemeral photons is: The pressure we get is To be compared to 1- Our starting hypotheses on ephemeral photons are not bad! Especially when we know that experiments seem to favor a slightly higher pressure than predicted by Casimir 2- Maxwell predicts that the vacuum pressure in a sphere tends to make it explode. Our prediction is exactly the opposite. + their life time to be: Regardons ce qui tombe sur P 2

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ULTRAFAST LASERS: Michigan group achieves laser intensity record In 2004 Yanovsky generated peak powers of 45 TW from Hercules, and focused pulses to a then-record intensity of W/cm 2. 2 After a regenerative Ti:sapphire amplifier boosted seed pulses to 40 mJ, the output was directed to a cryogenically cooled four-pass amplifier followed by a final two-pulse amplifier. A deformable mirror corrected wavefront distortion, and an f/0.6 off-axis parabolic mirror focused the beam to a 0.8 µm spot, with peak intensity of W/cm 2. However, amplified spontaneous emission from the system posed a problem. Amplifiers normally produce a prepulse of amplified spontaneous emission lasting around a nanosecond, which Yanovsky says is forever on the timescale of a femtosecond pulse. That prepulse is only about 10 –6 or 10 –7 the power of the femtosecond pulse, but when the system optics focus the main pulse to an intensity of W/cm 2 the prepulse is powerful enough to destroy the target before the main pulse reaches it. To overcome that problem, Yanovsky two years ago used a technique called cross-polarized wave generation to reduce amplified spontaneous emission to a level only 10 –11 of the femtosecond pulse. 3 Pumping up the pulse power Now his group has added a two-pass Ti:sapphire booster amplifier that pumps up the femtosecond pulse power by a factor of six at 0.1 Hz, generating 17 J pulses that, after compression, have peak power of 300 TW and a pulse width of 30 fs at a nominal center wavelength of 810 nm. Focusing those pulses onto a target with a f/1.0 parabolic mirror gives peak intensity of 2 × W/cm 2. Yanovsky explained that they chose not to use the f/0.6 lens because its focal length is so short that something is likely to obstruct the output before it reaches the target. If the technique can be extended to the shorter-focus lens, power density should reach 5 × W/cm 2. That intensity is close to the level of 1023 to 1024 W/cm 2 where interesting new physics is expected. Those power densities should produce radiation reaction effects that affect electron motion, offering a test of electrodynamic models that treat electrons as points. A more practical application of such intensities would be to accelerate protons or ions for cancer therapy. Penetrating the body requires electron energies of about 200 MeV, which now can only be achieved with expensive particle accelerators. Current laser acceleration is limited to about 50 MeVtoo low to make ions penetrate the body, but higher laser intensities could boost electron energies to the required 200 MeV range. It wont be easy to crank power up to that range. We are pretty much close to the limit on the focal spot, says Yanovsky; there is no room to go to mirrors faster than f/0.6 at 800 nm. Pulses might be squeezed down to 10 fs, which could yield up to a factor of three increase in peak power, but thats about the limit. Building a bigger laser in principle could yield as much pulse energy as you could afford, but reaching an energy sufficient to generate 100 pW would cost at least $100 million. The ultimate pulse intensity would be about W/cm 2 REFERENCES 1. V. Yanovsky et al., Optics Express 16, 2109 (Feb. 4, 2008) 2. S.-W. Bahk et al., Optics Lett. 29, 2837 (Dec. 15, 2004) 3. V. Chvykov et al., Optics Lett. 31, 1456 (May 15, 2006). The Lawrence Livermore National Laboratory (Livermore, CA) produced the first petawatt pulses a decade ago with chirped-pulse amplification, and other laboratories have followed. But those systems are limited to single shots because they use glass amplifiers, which dissipate waste heat slowly. Hercules uses Ti:sapphire amplifiers, with much better heat dissipation that allows a 0.1 Hz repetition rate imposed by the glass pump lasers, says coauthor Victor Yanovsky, who added that diode pumping of solid-state lasers might yield 100 J pulses at 10 Hz.

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ELI - THE EXTREME LIGHT INFRASTRUCTURE ELI is a European Project, involving nearly 40 research and academic institutions from 13 EU Members Countries, forming a pan-European Laser facility, that aims to host the most intense lasers world-wide. The facility, based on four sites, will be the first large scale infrastructure based on the Eastern part of the European Community and has obtained a financial committment exceeding 700 M. The European Commission has recently signed the approval for funding the first ELI-pillar, located in the Czech Republic, with a budget of nearly 290 M. The first three sites will be situated in Prague (Czech Republic), Szeged (Hungary) and Magurele (Romania) and should be operational in The fourth site will be selected in 2012 and is scheduled for commissioning in ELI-Beamlines Facility In the Czech Republic, Prague, the ELI pillar will focus on providing ultra-short energetic particle (10 GeV) and radiation (up to few MeV) beams produced from compact laser plasma accelerators to users. ELI-Attosecond Facility In Hungary, Szeged, the ELI pillar will be dedicated to extremely fast dynamics by taking snap-shots in the attosecond scale (a billion of a billion of second) of the electron dynamics in atoms, molecules, plasmas and solids. It will also pursue research in ultrahigh intensity laser. ELI-Nuclear Physics Facility In Romania, Magurele, the ELI pillar will focus on laser-based nuclear physics. For this purpose, an intense gamma-ray source is forseen by coupling a high-energy particle accelerator to a high-power laser. ELI-Ultra High Field Facility The highest intensity pillar location will be decided in The laser power will reach the 200 PW or times the power of the world electric grid. It will depend, among other things, on the laser technology development and validation. It could be built on one of the existing three sites or in a new country. With the possibility of going into the ultra-relativistic regime, ELI will afford new investigations in particle physics, nuclear physics, gravitational physics, nonlinear field theory, ultrahigh-pressure physics, astrophysics and cosmology (generating intensities exceeding 10²³ W/cm²).